Manufacture of diesel fuel



Patented Dec. 23, 1941 UFACTURE F DIESEL FUEL h Marcus T. Kendall, Lon

by mesne assignment This invention relates to the manufacture of Diesel fuel oil and the like from petroleum. It has to do particularly with a method of treating oil to stabilize it and inhibit increase in residual carbon-forming bodies during storage.

Broadly the invention contemplates distilling petroleum, such as California crude, to prepare a fraction of desired boiling point and viscosity characteristics and, without substantial delay, subjecting the resulting fraction to treatment with a substantially fresh caustic soda solution under moderate conditions of temperature.

More specifically, the invention involves distilling crude petroleumto produce a distillate fraction falling within the range of approximately 400 to 750 F. This distillate fraction is then treated with caustic soda solution having a gravity of between about 3 and Be. and at a temperature between about 120 F. and 140 F.

I have found it desirable in the case of preparing a stable Diesel fuel oil to subject the distillate fraction to caustic treatment substantially immediately after it is removed from the fractionating stills. In any event, it should be subjected to such treatment within a few hours, and, preferably, within not more than about '72 hours, from the time it is distilled from the crude petroleum. Otherwise, the oil will not be completely stabilized.

The distillate fraction as obtained from the crude has a satisfactory color, namely 1 to 3 A. S. T. M., and also has a low Conradson carbon content, usually not in excess of 0.01%.

However, the distillate apparently contains hydrocarbons or hydrocarbon compounds which gradually undergo a chemical change during storage of the oil. As a result, upon standing in storage from about three months to a year, it darkens in color to as low as 8 A. S. T. M. and increases in residual carbon content to as high as 0.20%.

I have found that by subjecting the distillate oil to contact with sodium hydroxide solution of around 3 to 10 B., at a temperature of around 120 to 140 F., the treated oil is stabilized with respect to color and residual carbon content, especially if the treatment follows shortly after the oil is distilled from the crude.

Moreover, it is desirable to employ fresh caustic solution for each batch of oil. I have found that while spent caustic solutions have some in hibiting qualities, nevertheless, fresh caustic solution is preferable from the standpoint of inhibiting increase in the residual carbon content of the oil. For example, it has been found that where g Beach, Calif., assignor,

s, to The Texas Company, New York, N. Y., a corporation of Delaware No Drawing. Application June 3, 1939, Serial No. 277,257

4 Claims. (Cl. 196-41) the same caustic solution is used asecond time, the carbon residue content of the treated oil remains low after about days in storage, but after that time it increases. However, bytreat ing the oil with fresh caustic of the concentration mentioned and at the specified temperature, the resulting treated oil has shown no substantial increase in residual carbon content during storage for more than a year.

It is apparently necessary to employ a caustic solution having a gravity of not less than 3 B., since weaker solutions have been found to be inelfective. The employment of solutions having a gravity greater than 10 B.. is not 'practical, particularly on account of emulsification occurring during treatment.

Treating temperatures below about F. appear to be ineffective and also promote emulsification with the reagent. On the other hand, if the treating temperature is substantially above 140 F. the color of the resulting oil is darkened and, in addition, the treated oil is not colorstable.

By Way of specific example, a Diesel fuel oil was prepared from a blend of Signal Hill and Santa Fe Springs crudes in the following manher:

A blend composed of approximately 60% 24 A. P. I. gravity Signal Hill crude and 40% 32 A. P. I. gravity Santa Fe Springs crude was charged to the crude stills. After removing a straight run gasoline of approximately 395 F. end boiling point and a kerosene of approximately 485 F. end boiling point, a straight run gas oil was fractionated from the crude having an initial boiling point of approximately 450 F. and an end point of approximately 700 F., with an average gravity of about 33.0 A. P. I.

This gas oil fraction comprises a Diesel fuel oil stock suitable for chemical treatment. The best results are obtained by charging this gas oil to the agitator for the caustic treatment within 72 hours (before excessive oxidation has taken place).

After charging the oil to the agitator, about 3% by volume of 5 B. gravity caustic soda solution (NaOH) is then added and agitated with the stock at atmospheric temperature. After a thorough agitation of approximately 20 minutes the mixture is heated by either circulating through a heater (or by means of a closed steam coil within the agitator) to a temperature of approximately F. Agitation is stopped and the major portion of the used caustic and sludge is drawn off from the agitator. The stock now receives a hot spray wash (Water heated to 140 F.) until all trace of caustic soda has been removed from the oil, when the batch in the agitator is dropped to a pan tank and allowed to settle bright.

As previously stated, gas oil (Diesel oil) so treated is not only very stable in color but resists oxidation and polymerization in storage so that there is practically no rise in the carbon residue content, even after a prolonged period in storage of the treated oil.

A caustic solution of about 5 B. gravity and amounting to approximately 3% by volume of the oil appears to be the most effective. It is contemplated, however, that the proportion and concentration may vary from this, depending upon the particular oil undergoing treatment.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore onlysuch limitations should be imposed as are indicated in the appended claims.

I claim:

1. A method of treating a petroleum distillate fraction boiling approximately within the range 400 to 750 F. to stabilize it and inhibit increase in residual carbon content to thereby produce a stable Diesel fuel, which comprises subjecting the distillate within not more than about 7-2 hours after it-has been distilled from the crude petroleum to contact with fresh unused aqueous caustic soda solution of about 3 to 10 B. gravityand at a temperature within the range 120 to 140 F.

2. In the process of manufacturing a Diesel fuel oil substantially stable against increase in residual carbon content during storage, the method which comprises distilling from crude petroleum a distillate fraction having a boiling range of approximately 400 to 750 F., subjecting said distillate without substantial delay to contact with fresh unused aqueous caustic soda solution of about 3 to 10 B. gravity, effecting said contact at a temperature within the range to F. and removing the used reagent and sludge.

3. In the process of manufacturing a Diesel fuel oilsubstantially stable against darkening or changing in color during storage, the method which comprises distilling from crude petroleum a distillate fraction having a boiling range of approximately 400 to 750 F., subjecting said distillate without substantial delay to contact with fresh unused aqueous caustic soda solution of about 3' to 10 B. gravity, effecting said contact at a temperature within the range 120 to 140 F. removing sludge resulting from said contact, and washing the treated oil from which the sludge has been removed with water at approximately the temperature prevailing during the caustic treatment to remove remaining caustic and sludge.

4. The method according to claim 1 in which the distillate is treated with fresh caustic soda solution within a few hours after the distillate has been formed.

MARCUS T. KENDALL. 

